Preservation of potential biosignatures in the shallow subsurface of Europa

Abstract

Jupiter’s moon Europa, which is thought to possess a large liquid water ocean beneath its icy crust, is one of the most compelling targets in the search for life beyond Earth. Its geologically young surface, along with a number of surface features, indicate that material from Europa’s interior may be emplaced on the surface. However, the surface is affected by the harsh radiation environment of Jupiter’s magnetosphere, which over time may lead to chemical alteration and destruction of potential biosignatures. We show that radiation dose rates are highly dependent on surface location. Radiation processing and destruction of potential biosignatures is found to be significant down to depths of ~1 cm in mid- to high-latitude regions, and to depths of 10–20 cm within ‘radiation lenses’ centred on the leading and trailing hemispheres. These results indicate that future missions to Europa’s surface do not need to excavate material to great depths to investigate the composition of endogenic material and search for potential biosignatures. A model reconstructs the radiation dose from both protons and electrons on Europa’s surface. Using laboratory data on irradiated amino acids, it shows that organics can be preserved at detectable levels at depths of just a few centimetres at mid-to-high latitudes and in young (<10-Myr-old) terrains.